Process for the vaporization of formamide



March 13, 1934. H. A. BOND PROCESS FOR THE VAPORIZA'I'ION OF PORMAMIDEFiled July 9, 1931 INVENTOR. W A. B01707 Patented Mar. 13, 1934 UNITEDSTATES PATENT FFIQE PROCESS FOR THE VAPORIZATION OF FORMAMIDEApplication July 9, 1931, Serial No. 549,585

Claims.

This invention relates to the vaporization of formamide and moreparticularly to the vaporization of formamide from metal Vaporizers.

" Because of its high boiling point, around 200 U C. at atmosphericpressure, and because of the decomposition of formarnide into carbonmonoxide and ammonia, when heated, the problem of vaporizing formamidehas heretofore presented considerable diiiiculty. To avoid thisdecomposition it has previously been proposed to vaporize formamide atreduced pressure and it has further been proposed to vaporize formamidefrom surfaces heated above 215 C. without allowing the substantialaccumulation of liquid forniamide on the vaporizing surface. Theheretofore proposed methods of vaporizing formamide are costly, requiremore or less elaborate apparatus, necessitate careful control andtherefore are not entirely satisfactory. Although the decomposition issmall, solids stick to the hot surface and heat conduction becomes poor.Moreover, there is tendency when the liquid strikes the hot surface forit to agglomerate in droplets which evaporate with explosive effect andgive uneven evaporation.

One object of this invention is to provide a process for vaporizingaccumulated liquid formamide from a metal surface without appreciabledecomposition of the formamide and at substantially atmosphericpressure. A further object of this invention is to simplify and improvethe vaporizing of formamide. Further objects will be apparenthereinafter.

The invention comprises vaporizing formamide from a heat conductingsurface upon which said formamide is allowed to accumulate in a shallowpool which covers a substantial portion of the surface. Metal surfacesare particularly useful since their rate of heat conduction is greaterthan that of other materials.

The accompanying drawing shows in crosssection an apparatus suitable forcarrying out the process of this invention. Referring to the drawing 1is a metal base plate in which are embedded electrical elements 2. Metalcover 3, of such construction as to form a vapor space 10, is flanged ontop of base plate 1. 4 is an inlet pipe for liquid formamide having itsterminus 5 within the cover 3 and close to the base plate 1; 6 is anoutlet pipe for formamide vapor; several openings as at 7 are providedin the base plate in which thermocouples or other temperature measuringdevices may be inserted; 8 is a well of metal extending into the outlettube into which a thermometer 9 is inserted.

The invention will now be further described in terms of the accompanyingdrawing.

Liquid formamide is flowed into the vaporizer through pipe l and spreadas a shallow pool over a portion of the massive base plate 1, which isheated by means of heating elements 2 to a temperature of preferablybetween about 200 to 400 C. The vaporizer is tilted or sloped toward theliquid inlet at an angle of a few degrees so that the liquid accumulatesnear the inlet end; this tilting or slope will cause a uniformhorizontal or transverse spread of liquid and favor the formation of ashallow pool with its deeper portions near the inlet end. It will befound in general that the shallow pool of liquid formamide may cover asubstantial portion of the vaporizing surface and may cover the entiresurface. The temperature of the vaporizer plate near the inlet end willordinarily be maintained at about the boiling point of formamide, whilenearer the exit end the temperature may be considerably higher, it mayattain 300 to 400 0., or even more, on those portions of the vaporizersurface which are not covered by liquid. I prefer to vaporize attemperatures of 200-400" C.

To further clarify the invention, a specific example is given below,which however, should not be taken to limit the invention to thespecific details shown therein.

Example An apparatus similar to that shown in the drawing was employedconsisting of a forged aluminum base plate 2" thick by 12" wide by 24"long. 12 nichrome heating elements extending transversely through thebase, having a capacity of about 2 kilowatts each at 110 volts wereuniformly spaced lengthwise of the base plate and embedded therein. Theformamide was introduced through an aluminum pipe in diameter whichterminated above the base plate 1. The outlet pipe for formamide vaporwas also aluminum and was 1%" in diameter.. Two thermocouples wereinserted in the holes provided in the base plate of the vaporizer, onenear the inlet end and a second beyond the edge of the liquid pool offorrnamide accumulated in the vaporizer. The apparatus was tilted at anangle of about 2 toward the inlet end. The entire vaporizer wasthoroughly insulated with powdered magnesia contained in a rectangularsheet iron shell surrounding the vaporizer.

A thermometer was inserted in the well at the outlet end to measure thetemperature of the formamide vapor produced. Liquid formamide vapor perday.

was flowed into the apparatus at the rate of 142 grams per minute andformamide vapor collected therefrom at substantially the same rate.Vaporization was carried out at substantially atmospheric pressure. Thetemperature near the inlet end and beneath the accumulated pool offormamide varied from 195 to 210 C. Tests indicated that about to of thevaporizing surface was covered by the liquid formamide. The averagetemperature of the vaporizer beyond the point occupied by the pool offormamide was 374 C. varying from 365 to 395 C. in a series ofmeasurements. The average temperature of the vapor in the outlet pipewas 280 C. This temperature is the average of several taken over a onehour period. Tests on the percentage decomposition of formaniide inapparatus of this type have shown that the loss was in all cases lessthan 1.5% and frequently as low as 0.5%.

While the apparatus has been described as made of aluminum, other metalswhich do not deleteriously affect the decomposition of formamide, forexample copper, brass, iron or steel may be used. A metal surfacecovered with an adherent nonreactive thin oxide layer, for example, ZnOor A1203 may also be used, subject to the same restrictions. Good heatconducting surfaces are preferable.

The dimensions of the vaporizer will depend upon the scale of operationdesired. I prefer to employ a relatively massive metal base plate tofacilitate heat transfer and ballast and to introduce the liquid at oneor more points close to the surface of said vaporizer base plate toavoid uneven spreading and spattering. The heating elements should bespaced and otherwise arranged to produce a uniform temperature over thevaporlzing surface. I have found it advisable to so arrange them thatwhen the apparatus is empty various parts of the vaporizing surface willnot show more than to C. difference in temperature when heat is applied.

The apparatus described above is capable of vaporizing up to 500 lbs. ormore of forrnamide This vaporizer is serviceable for any amount ofvaporization up to its full rated capacity which will be attained whenthe entire vaporizing surface is substantially covered by liquid. Thetemperature of the vaporizing will depend on the amount of formamidepresent and the rate of heat supply; if correct, this rate of heatingshould be such that should the formamide input cease such liquid asremains on the surface will be completely evaporated within 5-10minutes. The temperatiu'e may also be adjusted by heating so thatportions of the vaporizer surface not covered by liquid formamide willnot in general exceed 400 C., i. e., the surface of the vaporizer willvary from about the boiling point of formamide up to about 400 C. Therate of heating should permit vaporization to take place at a sufficientrate so that the liquid formamide does not remain exposed to hightemperatures for periods of more than 5 to 10 minutes and preferably notmore than l-2 minutes, since otherwise the rate of decomposition, whichis of the order of 1 to 2% per minute, may become excessive.

The advantages of this process he in its simplicity of operation and inthe effective and speedy evaporation of formamide without substantialdecomposition losses due to the formation of carbon monoxide andammonia. It is particularly useful where a rapid supply of substantiallypure formamide vapor is desired. It has been found to give excellentresults when. used in connection with a converter such as that describedin U. S. P. 1,675,366, wherein said vapors are converted to hydrocyanicacid and water by a process requiring formamide of high purity.

I claim:

1. A process for vaporizing formainide comprising maintaining a shallowpool of formamide over a substantial portion of a surface heated to atemperature above the atmospheric boiling point of formamide.

2. A process for vaporizing formamide comprising flowing liquidformamide over a metal surface heated to 200 to 400 C., and continuallymaintaining a shallow liquid pool on a substantial portion of saidsurface.

3. A process for vaporizing formamide comprising flowing liquidformamide over an aluminum surface heated to 200 to 400 C. andcontinually maintaining a shallow pool on a substantial portion of saidaluminum surface.

4. In the vaporization of formamide the step comprising exposing saidformamide in a shallow pool to a heated metal surface selected from thegroup consisting of aluminum, brass, copper, iron and steel.

5. In the vaporization of formamide the step comprising exposing saidformamide in a shallow pool to a heated metal surface selected from thegroup consisting of aluminum, brass, copper, iron and steel, saidsurface being coated with a thin adherent non-reactive oxide layer.

I-IARLAN A. BOND.

